Unauthorized incursions of aircraft and ground vehicles onto runways and taxiways can often have catastrophic results. The number of aircraft accidents that occur on the ground is nearly three times the number of aircraft accidents that occur in the air.
In degraded visual conditions the problem becomes even greater since the ground controller is often reliant on non-visual information such as voice communication from the cockpit crew reporting the aircraft's current position on the airport surface, or display information from a ground surveillance radar system. Unfortunately, only the largest airports in the United States have ground surveillance radar systems to aid the controller. The Federal Aviation Administration (FAA) is addressing this problem by installing ASDE-3 ground surveillance radars in twenty-nine U.S. airports and the FAA Training Academy. The remainder of the U.S. airports depend solely on the visual observations of the controller and position reports from pilots. The problem gets even worse. The majority of ground surveillance radar systems other than ASDE-3 are often over twenty-five years old, difficult to maintain, and provide ironically inadequate information in poor weather when radar is needed most. As a result, the controller in the tower is almost completely reliant on his visual observations and surface position reports from aircraft crews to provide situational awareness of the current state of the airport surface. In degraded visual conditions, the controller is literally often asking the question "where are you?" to aircraft crews to provide his situational awareness of the airport surface. As a result, the controller has to maintain a mental image of the airport surface, rather than having hard surveillance data available.
The current state of surface traffic control and several solutions to this problem are discussed in an article entitled "Airport Surface Traffic Automation" written by Ervin F. Lyon and published in The Lincoln Laboratory Journal, Volume 4, Number 2, 1991. The article discusses several alternatives such as the Airport Surface Traffic Automation (ASTA) plan of the Federal Aviation Administration, and the Airport Movement Area Safety System (AMASS) currently under development by Norden Systems, a subsidiary of the assignee of the present invention. AMASS operates in conjunction with the ASDE-3 ground surveillance radar which utilizes high resolution radar electronic surveillance data to provide tower controllers with all weather surface surveillance capability. AMASS processes the ASDE-3 data to detect and track airport ground traffic, predict where the ground traffic will be a fixed time later (e.g., 10 seconds), and alert controllers of possible runway incursions and ground collisions with sufficient time to allow corrective action to be taken. However, neither the AMASS nor the ASDE-3 currently include the ability to identify vehicles on the airport surface.
One proposed system for identifying (i.e., tagging) vehicles on the airport surface includes the use of a surface Mode-S beacon system having approximately "five to seven simple stationary antennas and associated electronics around the periphery of the airport". However, such a system is complex and expensive due to the need for several antennas and associated electronics placed about the surface of the airport. In addition, not all aircraft are required to be equipped with a Mode-S transponder. Furthermore, airport vehicles such as plows, catering trucks and tugs are not required to be equipped with any type of transponder.
In order to provide the advantages of vehicle identification to as many airports as possible, a lower cost identification system which can be integrated into existing systems is required to identify aircraft, thus improving airport traffic management and collision avoidance technology.